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In an experiment to measure the heat of reaction (ΔH) for the neutralisation of hydrochloric acid and sodium hydroxide solution, 100 cm³ of 1 M HCl solution was added to 100 cm³ of 1 M NaOH solution in a polystyrene container with a cardboard lid - Leaving Cert Chemistry - Question 3 - 2017
Question 3
In an experiment to measure the heat of reaction (ΔH) for the neutralisation of hydrochloric acid and sodium hydroxide solution, 100 cm³ of 1 M HCl solution was adde... show full transcript
Worked Solution & Example Answer:In an experiment to measure the heat of reaction (ΔH) for the neutralisation of hydrochloric acid and sodium hydroxide solution, 100 cm³ of 1 M HCl solution was added to 100 cm³ of 1 M NaOH solution in a polystyrene container with a cardboard lid - Leaving Cert Chemistry - Question 3 - 2017
Step 1
Was heat released or absorbed when the HCl and NaOH solutions reacted? Justify your answer.
Answer
Heat was released during the reaction between HCl and NaOH. This is confirmed by the observed increase in temperature of the solution, indicating that the reaction is exothermic. The temperature rise is due to the formation of water and the enthalpy change (ΔH) is negative, signifying that energy is released into the surroundings.
Step 2
What features of the apparatus described help prevent heat loss to the surroundings?
Answer
The apparatus includes insulation using a polystyrene container, which minimizes heat loss to the environment. The cardboard lid further helps in reducing heat escape by trapping warm air inside, thereby ensuring a more accurate measurement of the temperature change.
Step 3
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Step 6
What temperature rise would you expect to record?
Answer
The expected temperature rise when repeating the experiment with 0.5 M NaOH would be approximately 3.4 °C. This is because the concentration of NaOH is halved, leading to a smaller heat change compared to the previous 1 M concentration.
Step 7
Justify your answer.
Answer
The justification for the expected temperature rise of 3.4 °C lies in the principle of dilution. Since the same volume of acid is neutralized, but the base concentration is lower, there will be less heat released. This corresponds to the reduced number of moles of NaOH available to react with HCl, ultimately resulting in a lower temperature change.